The invention relates generally to suspension locking of work vehicles. More particularly it relates to automatic suspension locking of skid steer vehicles when the operator manipulates a manual input device.
Skid steer loaders are small highly maneuverable vehicles that are used in place of front end loaders, backhoes and the like in constricted environments. They are particularly useful due to their small size and maneuverability.
Their maneuverability is due to their method of steering. The wheels on one side of the vehicle (typically two) can be driven independently of the wheels on the other side of the vehicle. The wheels themselves are not steerable. In other words, they cannot be turned about a generally vertical axis with respect to the chassis.
To steer a skid steer vehicle, the wheels on one side of the vehicle are driven at a different speed than the wheels on the other side of the vehicle. In an extreme-case they are also driven in opposite directions. Thus, the wheels on one side can be driven forward as the wheels on the other side of the chassis are driven in reverse.
These different velocities (and/or different directions) cause the wheels to skid sideways as they rotate. As a result, one side of the vehicle advances faster than the other, and the vehicle turns. In the extreme case, when the wheels on either side are driven in opposite directions, the vehicle can rotate about a vertical axis within the perimeter of the vehicle""s chassis thereby giving it a turning radius of zero.
In addition to the maneuverability provided by the steering arrangement, skid steer vehicles also benefit from a narrow wheelbase and small width over wheels. A short wheelbase and small width over wheels permits the vehicle to be used in confined spaces, but prevents the use of sprung suspensions.
A sprung suspension used on a short wheelbase vehicle would cause excessive diving as the implement connected to the loader arms is used to engage the ground. When the bucket or other implement mounted on the loader arms of the skid steer vehicle are pressed downward against the ground or are used to lift an object or a load of dirt (for example) the forces generated by engagement with the ground could cause a short wheelbase vehicle such as a skid steer loader to pitch up and down precipitously.
For this reason, skid steer vehicles having a short wheelbase (such as the common skid steer loader) have never been equipped with sprung suspensions.
To permit the use of sprung suspensions in skid steer vehicles, such a suspension system needs to have the capability of locking the suspensions or wheels with respect to the chassis whenever the operator is engaged in such activities as digging, scooping, lifting, dumping, or lowering using the loader arms and bucket or other implement attached to the loader arms.
Any of these activities can cause the vehicle to pitch by reducing or increasing its total weight. Similarly, any ground engagement of the loader arms or implements (such as buckets) attached to the loader arms can also cause the vehicle to pitch.
It would therefore be desirable to provide a skid steer vehicle with a suspension system that is locked automatically whenever the operator moves or attempts to move the loader arms of the vehicle or moves the bucket (or other implement) attached to the loader arms. It is an object of this invention to provide such a skid steer vehicle.
In accordance with a first embodiment of the invention, a skid steer vehicle is provided that includes a chassis having a left side and a right side; at least one loader arm pivotally coupled to the chassis to pivot about a substantially horizontal axis; at least one hydraulic cylinder coupled to the at least one loader arm to raise and lower the at least one loader arm with respect to the chassis; an engine coupled to the chassis; first and second variable displacement hydraulic pumps coupled to the engine to provide two separately controllable sources of hydraulic fluid under pressure; four non-steerable and ground-engaging wheels coupled to the chassis to drive the vehicle over the ground, wherein the wheels are disposed two on each side of the chassis in a fore-and-aft relation; four control arms pivotally coupled to the chassis and coupled to the four wheels to permit the wheels to pivot at least in a vertical direction with respect to the chassis; at least two hydraulic motors for driving the wheels wherein at least one motor is driven by fluid from the first pump and in turn drives the wheels on the left side of the chassis and at least another motor is driven by fluid from the second pump and in turn drives the wheels on the right side of the chassis; four hydraulic cylinders, each cylinder operably coupled to one of the wheels to control at least the vertical position of the wheels with respect to the chassis; a first operator-actuable control configured to signal a desired movement of the at least one loader arm; and an electronic controller operably coupled to the first operator-actuable control to both (a) lock the four wheels in a vertical position with respect to the chassis and (b) move the at least one loader arm when the first operator-actuable control is manipulated by the operator.
The first operator-actuable control may be an elongate member having a neutral position and may be deflectable in a first direction from the neutral position to raise the loader arm, and may be deflectable in a second direction that is opposite the first direction to lower the loader arm. The first operator-actuable control may be configured to generate an electrical signal indicative of its degree of deflection away from the neutral position and the electronic controller may be configured to lock the four wheels and move the loader arm in response to the first operator-actuable control being moved by the operator away from the neutral position. The skid steer vehicle may further include a bucket pivotally coupled to the at least one loader arm; and at least one bucket cylinder coupled to the bucket to pivot the bucket with respect to the at least one loader arm. The first operator-actuable control may be movable in a third direction perpendicular to the first direction to pivot the bucket with respect to the at least one loader arm. The electronic controller may be configured to respond to deflection of the first-operator-actuable control in the third direction to both (a) lock the four wheels in a vertical position with respect to the chassis and (b) pivot the bucket with respect to the at least one loader arm. The electronic controller may be configured to unlock the four wheels for vertical movement with respect to the chassis in response to the first operator-actuable control returning to the neutral position.
In accordance with a second embodiment of the invention, a skid steer vehicle is provided that includes a chassis having a left side and a right side; at least one loader arm pivotally coupled to the chassis to pivot about a substantially horizontal axis; at least one hydraulic cylinder coupled to the at least one loader arm to raise and lower the at least one loader arm with respect to the chassis; an engine coupled to the chassis; first and second variable displacement hydraulic pumps coupled to the engine to provide two separately controllable sources of hydraulic fluid under pressure; four non-steerable and ground-engaging wheels coupled to the chassis to drive the vehicle over the ground, wherein the wheels are disposed two on each side of the chassis in a fore-and-aft relation; two control arms pivotally coupled to the chassis and coupled to the two forward wheels to permit the two forward wheels of the four wheels that are disposed on either side of the chassis to pivot at least in a vertical direction with respect to the chassis; at least two hydraulic motors for driving the wheels wherein at least one motor is driven by fluid from the first pump and in turn drives the wheels on the left side of the chassis and at least another motor is driven by fluid from the second pump and in turn drives the wheels on the right side of the chassis; two hydraulic cylinders, each cylinder operably coupled to one of the two forward wheels to control at least the vertical position of the two forward wheels with respect to the chassis; a first operator-actuable control configured to signal a desired movement of the at least one loader arm; and an electronic controller operably coupled to the first operator-actuable control to both (a) lock the two forward wheels in a vertical position with respect to the chassis and (b) move the at least one loader arm in response to operator manipulation of the first operator-actuable control.
The first operator-actuable control may be an elongate member having a neutral position and may be deflectable in a first direction from said neutral position to raise the loader arm, and may be deflectable in a second direction that is opposite the first direction to lower the loader arm. The first operator-actuable control may be configured to generate an electrical signal indicative of its degree of deflection away from the neutral position and the electronic controller may be configured to lock the two forward wheels and move the loader arm in response to the first operator-actuable control being moved by the operator away from the neutral position. The vehicle may further include a bucket pivotally coupled to the at least one loader arm; and at least one bucket cylinder coupled to the bucket to pivot the bucket with respect to the at least one loader arm. The first operator-actuable control may be movable in a third direction perpendicular to the first direction to pivot the bucket with respect to the at least one loader arm. The electronic controller may be configured to respond to deflection of the first-operator-actuable control in the third direction to both (a) lock the two forward wheels in a vertical position with respect to the chassis and (b) pivot the bucket with respect to the at least one loader arm. The electronic controller may be configured to unlock the two forward wheels for vertical movement with respect to the chassis in response to the first operator-actuable control returning to the neutral position.
In accordance with a third embodiment of the invention, a method of locking suspensions of a skid steer vehicle is provided for a skid steer vehicle including a chassis having a left side and a right side; at least one loader arm pivotally coupled to the chassis to pivot about a substantially horizontal axis; at least one hydraulic cylinder coupled to the at least one loader arm to raise and lower the at least one loader arm with respect to the chassis; an engine coupled to the chassis; first and second variable displacement hydraulic pumps coupled to the engine to provide two separately controllable sources of hydraulic fluid under pressure; four non-steerable and ground-engaging wheels coupled to the chassis to drive the vehicle over the ground, wherein the wheels are disposed two on each side of the chassis in a fore-and-aft relation; two control arms pivotally coupled to the chassis and coupled to the two forward wheels to permit the two forward wheels of the four wheels that are disposed on either side of the chassis to pivot at least in a vertical direction with respect to the chassis; at least two hydraulic motors for driving the wheels wherein at least one motor is driven by fluid from the first pump and in turn drives the wheels on the left side of the chassis and at least another motor is driven by fluid from the second pump and in turn drives the wheels on the right side of the chassis; two hydraulic cylinders, each cylinder operably coupled to one of the two forward wheels to control at least the vertical position of the two forward wheels with respect to the chassis; a first operator-actuable control configured to signal a desired movement of the at least one loader arm; and an electronic controller operably coupled to the first operator-actuable control, to said at least one hydraulic cylinder, and to said two hydraulic cylinders, wherein the method includes the steps of manually manipulating the first operator-actuable control to generate a signal indicative of an operator request to move said at least one loader arm; transmitting said signal indicative to the electronic controller; moving said at least one loader arm responsive to the signal indicative of the operator request; and locking the two forward wheels responsive to the signal indicative of the operator request.
The first operator-actuable control may be a joystick and the step of manually manipulating may include the step of moving the joystick to generate the signal indicative of an operator request to move said at least one loader arm. The vehicle may also include a bucket pivotally coupled to the at least one loader arm, and the method may further include the steps of manually manipulating the first operator-actuable control to generate a signal indicative of an operator request to move said bucket with respect to said loader arm; transmitting said signal indicative an operator request to move said bucket to the electronic controller; moving said bucket responsive to the signal indicative of the operator request to move said bucket; and locking the two forward wheels responsive to the signal indicative of the operator request to move the bucket.